Muni fiber: L1 or L2?

Fri Feb 1 23:33:40 UTC 2013

Owen DeLong <owen at delong.com> wrote:

> Nope The power going into each fiber out of the splitter is 1/16th
> that of what went into the splitter.

... which is 12 dB loss.

> Yes, your total in-line loss is still 10km, but you are forgetting
> about the fact that you lost 15/16th of the power effectively going
> to the fiber when you went through the splitter (in addition to the
> splitter loss itself).
> 
> So: CO Based splitter:
> 
> Each customer gets (IN - 16dB - (10km x .26db))/32

Each customer gets IN - ~0dB - 12 dB - 2.6 dB = IN - 14.6 dB.

> Splitter at 9km:
> 
> Each customer gets (IN - (9km x .26dB) -16db)/32-(1km x .26db)

Each customer gets IN - 2.34 dB - 12 dB - 0.26 dB = IN - 14.6 dB.

> If we use 5dBm as our input, this works out:
> 
> CO: (5db - 16db - (10km x .26db) / 32
> /32 is effectively -15 db (-3db = ½ power, 32 = 2^5)
> Substituting: (5db - 16db - 2.6db) -15db = -28.6db to each customer.
> 
> Spitter at 9km: (5db - (9km x .26db) -16db)/32-(1km x .26db)
> Substituting: (5db - 2.34db -16db)-15db-.26db = -28.08db to each customer
> 
> So there is a difference, but it seems rather negligible now that I've
> run the numbers.
> 
> However, it's entirely possible that I got this wrong somewhere,
> so I invite those more expert than I to review the calculations
> and tell me what I got wrong.

You are multiplying logarithmic values.

> Owen

--Johnny